The chain drive is extremely widely used for driving bicycles. In this context, the drive chain wheel which is connected to the pedal is positioned predominantly outside the bicycle frame from an axial perspective, whilst the drive crown gear mounted on the rear wheel axle is arranged predominantly within the bicycle frame between the bicycle frame and the rear wheel from an axial perspective.
Multi-gear shifters for bicycles are preferably implemented by way of chain drives having various chain wheels on the pedal and various crown gears on the rear wheel or by way of single-level chain drives in combination with hub transmissions in the rear wheel or by way of a combination of these two solutions. Thus, in total, overall transmission ratios of up to 1:4.9 (for example SRAM i-motion with the chain wheel combination 48/18) are achieved. To achieve expedient deployments (distance covered per pedal rotation) with an appropriate ratio between distance travelled and pedalling frequency, these shifting combinations are used for idle wheel sizes of 28 to 16 inches.
Bicycles having small idle wheels are preferably used so as to achieve small packaging sizes and weights, and are often in the form of folding bicycles. Bicycles having idle wheels of 14 inches and less require a transmission ratio between the pedal frequency and the idle wheel frequency of at least 1:5 so as to achieve an expedient deployment.
Moreover, trailer bicycles for bicycles are known, which are trailed on the rear of a bicycle and generally have much smaller idle wheels than the bicycles on which they trail. Until now, transmissions having similar transmission ratios to those of the bicycles themselves have generally been used for these trailer bicycles. Thus, the person who is riding on the trailer bicycle has to pedal at much higher pedal frequencies than the person on the bicycle on which the trailer bicycle trails. Even trailer bicycles with small idle wheels require the aforementioned transmission ratios between the pedal frequency and the idle wheel frequency.
To achieve the aforementioned overall transmission ratios of approximately 1:5 and less for bicycles having idle wheel sizes of 14 inches and less, the following solutions are known:    a. In particular for the idle wheel size of 14 inches, a chain drive is occasionally used, having a particularly large drive chain wheel (for example having 53 teeth) arranged outside the bicycle frame and a particularly small driven crown gear (for example having 11 teeth), the driven crown gear being arranged between the bicycle frame and the rear wheel in an axial perspective.    b. In the Dreamslide bicycle from Dreamslide S.A., Bures-sur-Yvette, France, a particularly large driving mechanism chain wheel and a particularly small driven crown gear are likewise used, the drive chain wheel and the driven crown gear being arranged inside the bicycle frame in an axial perspective.    c. Using two chain drives in succession (for example U.S. Pat. No. 3,623,749 A, EP 1 600 368 A2, U.S. Pat. Nos. 5,186,482 A, 7,229,089 B2, 6,595,539 B1, US 2005/0 035 570 A1, U.S. Pat. No. 6,799,771 B2).    d. Using a planetary gearing system having a stationary ring gear and a driven sun gear on the pedal in combination with a chain drive (DE 39 05 579 A1 and high speed drive from Schlumpf Innovations GmbH, Vilters/Switzerland).    e. Using a planetary gearing system having a stationary ring gear and a driven sun gear on the rear wheel in combination with a chain drive (for example DE 39 05 579 A1, and also U.S. Pat. No. 3,944,253 A in parts, FIG. 20 of WO 2011/102 606 A2).
Solution a. has the drawback that, because of the different arrangement of the drive chain wheel (outside) and the driven crown gear (inside) with respect to the bicycle frame, the bicycle frame has to be passed through between the chain wheels or over the chain drive. Because of a number of parameters (for example the large chain wheels required and the small driven crown gear, the frame shape, the required frame strengths, the required distance of the rear wheel from the bicycle frame, the arrangement of a suitable brake, the construction conditions for the rear wheel and the chain), in this context a minimum distance, which can be determined as a function of the idle wheel size, has to be maintained between the pedal axle and the rear wheel axle. In an embodiment as a folding bicycle, this minimum distance and the large drive chain wheel lead to a correspondingly large packaging size. By way of example, if a chain wheel combination of 53/11 is used, only an overall transmission ratio of 1:4.8 is achieved. There is therefore the further drawback that the achievable overall transmission ratio for idle wheel sizes smaller than 14 inches barely makes an appropriate deployment possible. Because of the resulting chain skew, an embodiment as a multi-gear derailleur gear set is only possible with a correspondingly long chain, and this in turn makes a determinable minimum distance necessary between the pedal axis and the rear wheel axis.
Solution b. has the following drawbacks:
The bicycle frame, the bottom bracket and the chain wheel have to be manufactured, mounted and maintained as separate components, at a correspondingly high cost. The special embodiment of the chain wheel prevents the use of multiple chain wheels. Likewise, because of the special drive chain wheel, the arrangement of the brakes and the requirements for the bicycle frame, a minimum distance, which can again be determined as a function of the idle wheel size, is necessary between the pedal axis and the rear wheel axis, and in an embodiment as a folding bicycle would in turn result in a correspondingly large packaging size.
Solution c. has the following drawbacks:
Because of the two chain drives which are to be implemented in series, the double chain drive requires a relatively large horizontal distance between the pedal axis and the rear wheel axis. As a result, the folded length of a folding bicycle is relatively large, and the directional stability is lessened as a result of the lower rider weight on the rear wheel. As a single-gear transmission, these solutions require at least two transmission ratios (2 chain drives). As a multi-gear transmission, these solutions would require at least three transmission ratios (2 chain drives and a multi-gear hub shifter in the rear wheel). The resulting high rotational speed of the second chain drive requires a high expenditure of energy.
Solution d. has the following drawbacks:
The torque is introduced from the pedal onto the pedal bearing shaft. Because of the high pedal forces which have not yet been transmitted and because of the relatively low diameter of the pedal bearing shaft, the shaft-hub connection between the pedal bearing shaft and the planet carrier of a downstream planetary gearing system has to be dimensioned correspondingly large, or be provided in a material fit as in DE 39 05 579 A1. The gearwheels which are to be used in the planetary gearing system on the pedal likewise have to be made relatively large and thus also relatively heavy. The resulting high rotational speed of the chain drive requires a high expenditure of energy.
The variant disclosed in DE 39 05 579 A1 in relation to solution e. has the following drawbacks:
The planet carrier of the planetary gearing system and the driven crown gear of the chain drive are positioned on different sides of the bicycle frame in an axial perspective. This results in the drawback that the torque of the driven crown gear initially has to be transmitted to the rear wheel shaft before it can be received on the other side of the bicycle frame by the planet carrier. The rear shaft and any shaft-hub connections between the driven crown gear and the rear wheel shaft or between the rear wheel shaft and the planet carrier have to be able to receive a high torque. Thus, either the planet carrier and the rear wheel shaft have to be produced in a single piece, as disclosed in DE 39 05 579 A1, resulting in very high material waste and costs for the rear wheel shaft, or a correspondingly large shaft-hub connection has to be provided between the rear wheel shaft and the planet carrier. Overall, the known variant makes a considerable axial installation space necessary between the chain line and the central reference plane of the bicycle. A further drawback is that, in the known solution, the bending moment acting on the rear wheel shaft as a result of the rider's weight also acts on the planet carrier and is detrimental to the tooth engagement of the planetary gearing system. In addition, with the arrangement of the planetary gearing system on the inside of the bicycle frame, only one gear ratio of the planetary gearing system can be implemented, since the arrangement of the driven sun gear as a sun gear mounted on the rear wheel shaft means that, as seen from the sun gear, the torque can only be transmitted in the axial direction with respect to the rear wheel.
The variants disclosed in U.S. Pat. No. 3,944,253 A or in DE 25 20 129 A1 and in FIG. 20 of WO 2011/102 606 A2 in relation to solution e. have the following drawbacks:
As a result of the different arrangement of the drive chain wheel (outside) and the driven crown gear (inside) with respect to the bicycle frame, the bicycle frame has to be passed through between the chain wheels, with the drawbacks described previously in point a. above. Moreover, with the arrangement of the planetary gearing system on the inside of the bicycle frame, only one gear ratio of the planetary gearing system can be implemented, since the arrangement of the driven sun gear as a sun gear mounted on the rear wheel axles means that, as seen from the sun gear, the torque can only be transmitted in the axial direction with respect to the rear wheel.